Non-aqueous electrolyte secondary batteries, or lithium ion secondary batteries have been widely used as power sources for mobile equipment such as mobile phones and notebook personal computers. Non-aqueous electrolyte secondary batteries are now indispensable for today's ubiquitous network society, for which further improvement in capacity is eagerly desired. Non-aqueous electrolyte secondary batteries have been recently employed as power sources for power tools. In the future, such non-aqueous electrolyte secondary batteries are expected to be used for wider applications including power sources for hybrid automobiles and the like.
Until today since the mass production of lithium ion secondary batteries started in 1991, the battery energy density has been doubled from 280 Wh/L to 580 Wh/L. In those years, there has been no change in the basic design using LiCoO2 for a positive electrode active material and graphite for a negative electrode. In contrast, the techniques for improving the battery structure and for increasing the capacity have been advanced and there is little or no room left for improvement. As such, the development of new materials with high capacity, high performance, and high level of safety is expected.
Under these circumstances, studies have been actively conducted on ternary-system lithium-containing composite oxides containing three elements of nickel, manganese, and cobalt as a promising material that will replace LiCoO2. Typical techniques relating to ternary-system lithium-containing composite oxides are disclosed in the following documents.    [Patent Document 1] U.S. Pat. No. 6,660,432    [Patent Document 2] U.S. Pat. No. 6,964,828    [Patent Document 3] U.S. Pat. No. 5,718,989    [Non-Patent Document 1] T. Ohzuku and Y. Makimura, Chem. Lett., 642 (2001)